Film process

ABSTRACT

A controlled permeability film and process for producing same wherein the film includes: a film forming polyolefin polymer; and an inert porous filler in an amount effective to reduce the ratio of the carbon dioxide permeability and water permeability to the oxygen permeability of the film, wherein the filler has a particle size greater than the intrinsic film thickness of the film forming polymer; the controlled permeability film being further modified to reduce the CO 2  /O 2  permeability ratio to approximately 0.5 to 2.0.

The present invention relates to a method of producing improvedcontrolled permeability films and to improved films produced thereby.

Control of carbon dioxide (CO₂) and/or oxygen (O₂) concentration aroundstored products has been shown in the prior art to increase the storagelife thereof. For example conditions for the optimal storage ofhorticultural commodities are influenced by factors which include cropspecies, cultivar, growing conditions, maturity, quality, temperature,relative humidity, packaging, and storage duration. Storage undercontrolled and modified atmosphere is influenced by the concentration ofoxygen, carbon dioxide, ethylene, water vapour and other gases.Controlled atmosphere (CA) storage is achieved by externally supplying agas stream of the required O₂ and CO₂ concentration into the storagecold room. Controlled atmosphere research into broccoli, for example,has shown that oxygen levels below approximately 1% and CO₂ levelshigher than approximately 15% independently induce offensive off-odoursand off-flavours. Reported optimum O₂ and CO₂ concentrations forbroccoli range from approximately 1 to 2.5% and approximately 5 to 10%respectively. Controlled atmosphere packaging achieves extended producelife because of effects such as slowing respiration and inhibitingpathogen growth.

It is also known in the prior art that CO₂ and O₂ atmospheressurrounding produce can be modified by utilizing the respirationbehaviour of the produce where O₂ is converted to CO₂. With modifiedatmosphere (MA) packaging, produce is stored in polymeric film where thefilm permeability is exactly matched to the expected respirationbehaviour as influenced by temperature and atmosphere changes to providethe optimum CO₂ and O₂ atmosphere. The accumulated O₂ and CO₂concentration in such a package will be related to the rate at which O₂and CO₂ is consumed or generated by the produce and the containerpermeability by a simple mass balance. The sensitivity of this balanceto O₂ and CO₂ permeability and the possibility of producing commoditypolymer films requires highly consistent and economic manufacturing ofcontrolled permeability films.

Another use of controlled permeability films is for the storage ofnematodes. As disclosed in co-pending application number PCT/AU92/00041,the entire disclosure of which is incorporated herein by reference,nematodes may be successfully packed for storage and transport usingfilms according to the present invention.

In International Patent Application PCT/AU91/00346, to the applicants,the entire disclosure of which is incorporated herein by reference,there is disclosed a controlled permeability film including a filmforming polymer and optionally including a dispersing polymer; and aninert porous filler optionally having a surface modifying agent coatedthereon, the inert porous filler being present in an amount effective toreduce the ratio of the carbon dioxide permeability to the oxygenpermeability of the film, and wherein the filler has a particle sizegreater than the intrinsic film thickness of the film forming polymer. Acomposite packaging article and a packaged produce product are alsodisclosed.

Such films of controlled permeability have been partially successful,however, their success has been limited by a continued difficulty inproducing consistent film permeabilities throughout the film anddifficulties in controlling film thickness.

Accordingly it is an object of the present invention to overcome, or atleast alleviate, one or more of the difficulties related to the priorart.

Accordingly, in a first aspect of the present invention there isprovided a controlled permeability film including;

a film forming polyolefin polymer; and

an inert porous filler in an amount effective to reduce the ratio of thecarbon dioxide (CO₂) permeability to the oxygen (O₂) permeability of thefilm, wherein the filler has a particle size greater than the intrinsicfilm thickness of the film forming polymer; the controlled permeabilityfilm being further modified to reduce the CO₂ /O₂ permeability ratio toapproximately 0.5 to 2.0.

Preferably the CO₂ /O₂ permeability ratio is reduced to approximately0.5 to 1.5.

It is noted that the CO₂ /O₂ permeability ratio of most unmodifiedpolymers is in the order of 4 to 6.

It will be further understood that a reduced permeability ratio resultsin a film having a more consistent permeability performance throughout.

In a further aspect of the present invention a process for preparing acontrolled permeability film which includes providing

a film forming polyolefin polymer; and

an inert porous filler in an amount effective to reduce the ratio of thecarbon dioxide (CO₂) permeability to the oxygen (O₂) permeability of thefilm, and wherein the filler has a particle size greater than theintrinsic film thickness of the film forming polymer;

mixing the polyolefin polymer and inert porous filler at elevatedtemperature;

forming the mixture into a film; and

subjecting the film to a permeability modifying step such that the CO₂/O₂ permeability ratio is reduced to approximately 0.5 to 2.0.

The permeability modifying step may include a pressure treatment, a heattreatment or stretching treatment, or a combination thereof.

In a preferred form the permeability modifying step may includecontacting the film with a pressure plate or roller.

The contacting step may be conducted at room temperature or at elevatedtemperature. The contacting step may be conducted at a temperature offrom approximately 10° C. to 200° C., preferably approximately 75° C. to115° C.

The pressure plate or roller may apply a compressive force to the film.The compressive force is preferably sufficient to thin or remove filmforming material between the filler particles and the surroundingatmosphere. The compressive force applied may be in the rangeapproximately 2.5 kg to 100 kg, preferably approximately 5 kg to 75 kg.

A roller treatment is preferred as this may provide a film having a moreconsistent thickness.

Alternatively, or in addition, the permeability modifying step mayinclude subjecting the film to a uniaxial stretching.

The stretching force applied may be approximately 2.5 kg to 75 kg,preferably approximately 5 kg to 50 kg.

The term "intrinsic film thickness" as used herein refers to thecalculated thickness of the polymeric film. The intrinsic film thicknessis the thickness the polymer would have if the filler was not there.

By the term "film" as used herein we mean a film, sheet or like article.

The film forming polyolefin polymer of the controlled permeability filmmay be of any suitable type. The film forming polymer may be selectedfrom polyethylene and blends of polyethylene with polyesters includingpolyethylene terephthalate and polybutylene terephthalate, vinylpolymers including polyvinyl chloride, polyvinyl acetate, ethylene-vinylacetate copolymers and ethylene-vinyl alcohol copolymers, polycarbonatesand polystyrenes and polyalkylene oxide polymers, including polyethyleneoxide polymer. Preferably the film forming polyolefin is a polyethylene,more preferably a low density polyethylene.

The inert porous filler may be of any suitable type. The inert porousfiller may be an organic or inorganic filler. The inert porous fillermay be a naturally-occurring porous material or synthetic porousmaterial. The naturally-occurring porous materials may be selected frominorganic materials, such as pumice, tuff, rhyolite, dacite, reticulite,scoria, lapilli, agglomerate, perlite, pumicite, other volcanic rocks,natural zeolites or sandstones and organic materials, such as coal,char, charcoal, starch, seaweed, polymeric carbohydrates. The syntheticmaterials may be selected from porous glasses such as "Vycor", claysmodified to produce porosity, silicate phases, such as cordierite ormullite or metal oxides, such as alumina, silica, zirconia or magnesia,or cerium compounds, or hydrophilic organic polymers, such as polyvinylalcohol or polyacrylamide. Synthetic metallic compounds such as alumina,aluminum isopropoxide and Ce(NO₃)₃ derivatives may be used as describedbelow. Inorganic fillers selected from alumina, silica, pumice, naturalzeolites or derivatives thereof are preferred.

A mineral filler is preferred for modifying CO₂ /O₂ permeability ratios.A pumice product may be used. Particles having a particle size greaterthan the intrinsic film thickness of the film forming polymer has beenfound to be particularly suitable. Whilst we do not wish to berestricted by theory, it is postulated that filler particles having adiameter greater than the intrinsic film thickness of the film formingpolymer may provide improved properties including higher permeabilities,better permeability-temperature behaviour, more consistent filmproperties and better carbon dioxide/oxygen permeability ratios.

In a preferred aspect of the present invention the inert porous fillermay be modified to alter its permeability characteristics. The inertporous filler may be subjected to leaching and/or burning treatment toincrease porosity. The inert porous filler may be modified to render ithydrophobic.

Accordingly, in a further aspect of the present invention the inertporous filler includes a surface modifying agent coated thereon in anamount effective to modify the surface behaviour of the porous filler.

In a preferred aspect, the modified porous filler is present in anamount sufficient to reduce the carbon dioxide to oxygen permeabilityratio of the controlled permeability film.

The surface modifying agent may reduce the adhesion of the film formingpolymer to the porous filler, which may result in the formation ofdepressions in the film.

The depressions may impart microperforations to the controlledpermeability film. The net effect of the surface modifying agent is thusa reduction in the effective film thickness. The carbon dioxide tooxygen permeability ratio for the controlled permeability film may alsobe altered.

The surface modifying agent may be any suitable agent capable ofmodifying the surface of the inert porous filler. Preferably, the agentis suitable to render the surface of the porous filler hydrophobic. Thesurface modifying agent may be an organic or an inorganic polymericmaterial, for example polyolefins, particularly polyethylenes, andoxygenated polyethylene for example polyethylene glycols, nonyl phenylpolyethylene oxide, polyvinyl alcohols, polyvinyl acetates, paraffins,polysiloxanes and silane coupling agents, metal alkoxides such as thoseof titanium and aluminium, alcohols such as n-butanol, and combinationsthereof.

The surface modifying agent should be used in a sufficient amount tocoat at least 10% of the surface of the inert porous filler. The surfacemodifying agent or combination of surface modifying agents may be addedin quantities greater than needed to coat the total surface so as tofill or partially fill the available pore volume.

In an alternative aspect of the present invention there is provided acontrolled permeability film composition including

a composite film including

a film forming polyolefin polymer; and

a dispersing polymer; and

an inert porous filler in an amount effective to reduce the ratio of thecarbon dioxide (CO₂) permeability to the oxygen (O₂) permeability of thefilm, and wherein the filler has a particle size greater than theintrinsic film thickness of the composite film; the controlledpermeability film being further modified to reduce the CO₂ /O₂permeability ratio to approximately 0.5 to 2.0.

Generally, the dispersing polymer should not be compatible with the filmforming polymer so that with appropriate blowing techniques, it formsdistinct sections within the composite film. The inclusion of adispersing polymer may affect the characteristics of the polymeric film.For example, where a linear low density polyethylene (LLDPE) film hasbeen combined with a less dense polyethylene (e.g. linear very lowdensity polyethylene) this may lead to an increase in the oxygenpermeability of the film. The inclusion of a less viscous polyethylene(e.g. high pressure low density polyethylene) may lead to a thinning ofthe film.

Suitable polymeric material that may be combined to form a compositefilm include polyolefins of differing grades. Particularly preferredpolyolefins are polyethylenes and oxygenated polyethylenes,polypropylene, polyesters including polyethylene terephthalate andpolybutalene terephthalate, vinyl polymers including polyvinyl chloride,polyvinyl acetate, ethylene-vinyl acetate copolymers and ethylene-vinylalcohol copolymers, polycarbonates and polystyrene, polyalkyleneoxidepolymers including polyethylene oxide polymer; and mixtures thereof.

A composite film may comprise 2 or more polymers blended together.

The most preferred blended films may be selected depending upon thedesired characteristics of the film. It is preferred that a compositefilm comprise 30 to 99% by weight based on the total weight of thecomposite film of a polyolefin polymer; and

approximately 1 to 70% by weight based on the total weight of thecomposite film of a dispersing polymer selected from polyolefins,polyesters, vinyl polymers, polycarbonates, polystyrenes, polyalkyleneolefin polymers and mixtures thereof.

According to a further preferred aspect of the present invention, thereis provided a controlled permeability film including

a composite film including

a film forming polyolefin polymer; and

a dispersing polymer; and

a modified porous filler in an amount effective to reduce the ratio ofcarbon dioxide to oxygen permeability of the controlled permeabilityfilm including

an inert porous filler wherein the filler has

a particle size greater than the intrinsic film thickness of thecomposite film, and

a surface modifying agent; the controlled permeability film beingfurther modified to reduce the CO₂ /O₂ permeability ratio toapproximately 0.5 to 2.0.

Modifications of both the composite film and porous filler may provideimproved properties, for example, higher permeabilities, betterpermeability/temperature behaviour, more consistent film properties andbetterCO₂ /O₂ permeability ratios.

In a preferred aspect of the present invention the controlledpermeability film may be utilised in the packaging of product includinghighly sensitive produce such as broccoli, or organisms such asnematodes. Accordingly in a preferred form there is provided a packagedproduct including

a controlled permeability film as described above; and

a product packaged therein.

The controlled permeability film may be utilised in the packaging ofhighly sensitive produce such as broccoli, or organisms such asnematodes.

The produce packaged may be of any suitable type sensitive to oxygendeterioration. The produce may be selected from broccoli, brusselssprouts, beans, cabbage, chicory, celery, cauliflower, radish,artichoke, lettuce, tomato, pepper, leeks, parsley, spinach, asparagus,mushroom and okra, flowers, berries, cherry, melons, mango, papaya,pineapple, avocado, persimmon, grapefruit, kiwi, nectarine, peach,apple, banana, orange, apricot, grape, cranberry, plum, pear and nashi.

The packaged produce product has been found to exhibit improved CO₂ /O₂permeability such that the deterioration of the produce product issignificantly reduced. It will be recognised that the atmospheric oxygenand CO₂ concentrations may be optimised to be within the optimum rangesfor a produce product. Reported optimum O₂ and CO₂ concentrations forbroccoli range from approximately 1 to 2.5% and approximately 5 to 10%respectively. It is postulated that the controlled permeability packageachieves extended produce life because of a slowing in respiration andinhibition of pathogen growth.

The concentration of carbon dioxide will be controlled by therespiration rate of the produce less the amount of CO₂ released throughthe film. This may be expressed ##EQU1##

The concentration of oxygen is directly related to the permeance of thefilm to oxygen.

Thus variation in the ratio of permeability of CO₂ /O₂ provides anability to produce a film having optimum characteristics for any chosenproduce.

The controlled permeability film utilised in this aspect of the presentinvention is preferably a polyethylene film, more preferably a lowdensity polyethylene (LDPE) film. The porous filler utilised in thisaspect of the present invention may be a pumice filler. It has beenfound that the broccoli produce may be packaged with loadings ofapproximately 6 to 7 kilograms per square meter utilising the controlledpermeability film according to the present invention. It will beunderstood that the mass of produce stored relative to the area ofpolymer film available for gases to pass through is an importantparameter effecting internal package atmosphere. Zagory et. al. (Proc.5th Int. CA Conference, Jun. 14-16, 1989, Wenatchee, Washington)packaged broccoli at loadings of approximately 3.2 to 4.5 kilograms persquare meter of polymeric film. Such loading ranges were found to beineffective in producing optimum CO₂ and O₂ concentration.

The organisms packaged may be of any kind requiring high levels ofmoisture and sufficient oxygen. The organisms may be selected fromnematodes, live aquatic animals or plants; and aerobic microorganisms.

The packaged organism product has improved permeabilities so thatpackaged organisms have improved survival and/or less maintenancerequirements. For nematodes, preferred transmission rates for oxygen andcarbon dioxide are:

O₂ -greater than 1.2×10⁻¹⁷

CO₂ -greater than 4×10⁻¹⁷

These values ensure that adequate oxygen is available and that moisturelevels are maintained in the packaged organism product. Packaging ofother organisms can be achieved by adjusting permeability ratios andfilm thickness to achieve the optimum transmission rates for a givenorganism.

For nematode storage, films having porous fillers with a pore size ofapproximately 0.1 μm are preferred. Particularly preferred are aluminaparticles having a particle size of from 53 μm to 75 μm and a pore sizeof 0.1 μm. The films used for nematode storage are preferablypolyethylene films, more preferably low density polyethylene (LDPE)films. In particularly preferred embodiment, a composite film of LDPEand ultralow density polyethylene is used.

Whilst the invention has been described with reference to its use as acontrolled atmosphere packaging for produce or organisms it should beunderstood that the applications for the controlled permeability filmare not restricted thereto. Other envisioned uses for controlledpermeability films are:

monitoring respiration rates where respiration rate can be determinedfrom the known permeability of the film and accumulation of respirationgases;

enhancing sorbent, scavenging, or indicating polymer additives wherepermeation of gases or liquids through the polymer is limiting theeffectiveness of the additive;

for use in co-extruded products where the different permeabilities arerequired for each layer of the multilayer film;

for packaging of meat, poultry, dairy or fish products;

for packaging of medicines, pharmaceuticals; microorganism culturemedia;

for packaging of live organs;

energy absorbing packaging; collapsible or elastic porosity can be builtinto the film simultaneously with the controlled permeability;

sachet material or similar coating material for example for containinggas sorbing or generating materials; such as sachets which may be placedinside produce container thereby modifying the atmosphere. It ispossible to combine the controlled permeability film according to thepresent invention with other films having preferred characteristics suchas high clarity or the like.

Thus according to a further aspect of the present invention there isprovided a composite packaging article including

a controlled permeability film as described above;

a packaging film adhered along at least one edge thereof to thecontrolled permeability film.

It will be understood that in this form the controlled permeability filmmay be used on a surface of the composite packaging article and adifferent packaging film on another surface. For example a high densityfilm may be used on one surface for display purposes for example a highclarity high density polyethylene film, with the controlled permeabilityfilm on another surface.

In a still further aspect of the present invention, there is provided acomposite packaging article including a controlled permeability film asdescribed above;

a sachet or like article attached to a surface of the controlledpermeability film, and including a gas sorbing or generating material.

The sachet or like article may be attached to the film in any suitablemanner. The sachet may be welded or attached utilising a suitableadhesive.

The gas sorbing material contained in the sachet may include a syntheticdouble-layered permanganate material of the type described inInternational Patent Application PCT/AU91/00246 to applicants.

The present invention will now be more fully described with reference tothe accompanying examples. It should be understood, however, that thedescription following is illustrative only and should not be taken inany way as a restriction on the generality of the invention describedabove.

EXAMPLE 1

A polyethylene film 15% low density and 85% linear low density wasfabricated according to PCT/AU91/00346 with 2% scoria. The intrinsicfilm thickness was 30 micron and the particle size was 50 to 75 micron.The film was processed by passing it between two stainless steel rollerseach weighing approximately 7 Kg. The rollers can be set with apredetermined distance between them and the bottom roller can moveagainst two springs with spring constants of 0.54 Kgmm⁻¹. The rollerscan be maintained at an elevated temperature by passing thermostaticallycontrolled heated oil through them. In this example, the rollers were atambient temperature with a spacing of 40 micron. The O₂ and CO₂permeabilities prior to this treatment were 2.5×10⁻¹⁵ and 6.7×10⁻¹⁵mole.m⁻¹ s⁻¹ Pa⁻¹ and afterwards 1.6×10⁻¹⁴ and 1.6×10⁻¹⁴ mole.m⁻¹ s⁻¹Pa⁻¹.

EXAMPLE 2

As in Example 1 except the roller spacing was 80 micron. The O₂ and CO₂permeabilities prior to this treatment were 2.5×10⁻¹⁵ and 6.7×10⁻¹⁵mole.m⁻¹ s⁻¹ Pa⁻¹ and afterwards 2.2×10⁻¹⁵ and 5.5×10⁻¹⁵ mole.m⁻¹ s⁻¹Pa⁻¹.

EXAMPLE 3

As in Example 1 except the film thickness was 20 micron. The film wasprocessed with the rollers heated to 80° C. and a roller spacing of 0micron. The O₂ and CO₂ permeabilities prior to this treatment were2.5×10⁻¹⁵ and 6.7×10-15 mole.m⁻¹ s⁻¹ Pa⁻¹ and afterwards 1.0×10-13 and1.1×10⁻¹³ mole.m⁻¹ s⁻¹ Pa⁻¹.

EXAMPLE 4

As in Example 1 except the film was processed with the rollers heated to80° C. and a roller spacing of 0 micron. The O₂ and CO₂ permeabilitiesprior to this treatment were 2.5×10⁻¹⁵ and 6.7×10⁻¹⁵ mole.m⁻¹ s⁻¹ Pa⁻¹and afterwards 3.2×10⁻¹ and 3.1×10⁻¹³ mole.m⁻¹ s⁻¹ Pa⁻¹.

EXAMPLE 5

As in Example 4 except the roller spacing was 40 micron. The O₂ and CO₂permeabilities prior to this treatment were 2.5×10⁻¹⁵ and 6.7×10⁻¹⁵mole.m⁻¹ s⁻¹ Pa⁻¹ and afterwards 4.4×10⁻¹⁴ and 3.4×10⁻¹⁴ mole.m⁻¹ s⁻¹Pa⁻¹.

EXAMPLE 6

As in Example 4 except the roller spacing was 80 micron. The O₂ and CO₂permeabilities prior to this treatment were 2.5×10⁻¹⁵ and 6.7×10⁻¹⁵mole.m⁻¹ s⁻¹ Pa⁻¹ and afterwards 2.4×10⁻¹⁵ and 6.5×10⁻¹⁵ mole.m⁻¹ s⁻¹Pa⁻¹.

EXAMPLE 7

As in Example 4 except the intrinsic film thickness was 50 micron. TheO₂ and CO₂ permeabilities prior to this treatment were 1.8×10⁻¹⁵ and5.6×10⁻¹⁵ mole.m⁻¹ s⁻¹ Pa⁻¹ and afterwards 1.7×10⁻¹³ and 2.0×10-1mole.m⁻¹ s⁻¹ Pa⁻¹.

EXAMPLE 8

As in Example 4 except the intrinsic film thickness was 80 micron. TheO₂ and CO₂ permeabilities prior to this treatment were 1.1×10⁻¹⁵ and4.0×10⁻¹⁵ mole.m⁻¹ s⁻¹ Pa⁻¹ and afterwards 2.7×10⁻¹⁵ and 4.9×10⁻¹⁵mole.m⁻¹ s⁻¹ Pa⁻¹.

EXAMPLE 9

As in Example 8 except the roller spacing was 80 micron. The O₂ and CO₂permeabilities prior to this treatment were 1.1×10⁻¹⁵ and 4.0×10¹⁵mole.m⁻¹ s⁻¹ Pa⁻¹ and afterwards 1.8×10⁻¹⁵ and 4.2×10⁻¹⁴ mole.m⁻¹ s⁻¹Pa⁻¹.

EXAMPLE 10

A polyethylene film 15% low density and 85% linear low density wasfabricated according to PCT/AU91/00346 with 0.5% scoria. The intrinsicfilm thickness was 20 micron and the particle size was 50 to 75 micron.The film was processed with the rollers at ambient temperature and aroller spacing of 0 micron. The O₂ and CO₂ permeabilities prior to thistreatment were 2.5×10⁻¹⁵ and 6.7×10⁻¹⁵ mole.m⁻¹ s⁻¹ Pa⁻¹ and afterwards1.7×10⁻¹⁴ and 1.3×10⁻¹⁴ mole.m⁻¹ s⁻¹ Pa⁻¹.

EXAMPLE 11

As in Example 10 except the intrinsic film thickness was 30 micron. TheO₂ and CO₂ permeabilities prior to this treatment were 2.5×10⁻¹⁵ and6.7×10⁻¹⁵ mole.m⁻¹ s⁻¹ Pa⁻¹ and afterwards 5.7×10⁻¹⁴ and 3.7×10⁻¹⁴mole.m⁻¹ s⁻¹ Pa⁻¹.

EXAMPLE 12

As in Example 11 except the roller spacing was 40 micron. The O₂ and CO₂permeabilities prior to this treatment were 2.5×10⁻¹⁵ and 6.7×10⁻¹⁵mole.m⁻¹ s⁻¹ Pa⁻¹ and afterwards 1.2×10⁻¹⁴ and 8.4×10⁻¹⁵ mole.m⁻¹ s⁻¹Pa⁻¹.

EXAMPLE 13

As in Example 11 except the roller spacing was 80 micron. The O₂ and CO₂permeabilities prior to this treatment were 2.5×10⁻¹⁵ and 6.7×10⁻¹⁵mole.m⁻¹ s⁻¹ Pa⁻¹ and afterwards 1.9×10⁻¹⁵ and 4.8×10⁻¹⁵ mole.m⁻¹ s⁻¹Pa⁻¹.

EXAMPLE 14

As in Example 10 except the film thickness was 50 micron. The O₂ and CO₂permeabilities prior to this treatment were 1.8×10⁻¹⁵ and 5.6×10⁻¹⁵mole.m⁻¹ s⁻¹ Pa⁻¹ and afterwards 1.8×10⁻¹⁴ and 1.4×10⁻¹⁴ mole.m⁻¹ s⁻¹Pa⁻¹.

EXAMPLE 15

As in Example 10 except the rollers were heated at 80° C. The O₂ and CO₂permeabilities prior to this treatment were 2.5×10⁻¹⁵ and 6.7×10⁻¹⁵mole.m⁻¹ s⁻¹ Pa⁻¹ and afterwards 1.2×10⁻¹³ and 7.0×10⁻¹⁴ mole.m⁻¹ s⁻¹Pa⁻¹.

EXAMPLE 16

As in Example 15 except the intrinsic film thickness was 30 micron. TheO₂ and CO₂ permeabilities prior to this treatment were 2.5×10⁻¹⁵ and6.7×10⁻¹⁵ mole.m⁻¹ s⁻¹ Pa⁻¹ and afterwards 7.8×10⁻¹⁴ and 5.7×10⁻¹⁵mole.m⁻¹ s⁻¹ Pa⁻¹.

EXAMPLE 17

As in Example 16 except the roller spacing was 40 micron. The O₂ and CO₂permeabilities prior to this treatment were 2.5×10⁻¹⁵ and 6.7×10⁻¹⁵mole.m⁻¹ s⁻¹ Pa⁻¹ and afterwards 1.1×10⁻¹⁴ and 8.8×10⁻¹⁵ mole.m⁻¹ s⁻¹Pa⁻¹.

EXAMPLE 18

As in Example 16 except the roller spacing was 80 micron. The O₂ and CO₂permeabilities prior to this treatment were 2.5×10⁻¹⁵ and 6.7×10⁻¹⁵mole.m⁻¹ s⁻¹ Pa⁻¹ and afterwards 3.7×10⁻¹⁵ and 6.8×10⁻¹⁵ mole.m⁻¹ s⁻¹Pa⁻¹.

EXAMPLE 19

As in Example 15 except the intrinsic film thickness was 50 micron. TheO₂ and CO₂ permeabilities prior to this treatment were 1.8×10⁻¹⁵ and5.6×10⁻¹⁵ mole.m⁻¹ s⁻¹ Pa⁻¹ and afterwards 2.2×10⁻¹⁴ and 2.1×10⁻¹⁴mole.m⁻¹ s⁻¹ Pa⁻¹.

EXAMPLE 20

As in Example 15 except the intrinsic film thickness was 80 micron. TheO₂ and CO₂ permeabilities prior to this treatment were 1.1×10⁻¹⁵ and4.0×10⁻¹⁵ mole.m⁻¹ s⁻¹ Pa⁻¹ and afterwards 0.9×10⁻¹⁵ and 3.2×10⁻¹⁵mole.m⁻¹ s⁻¹ Pa⁻¹.

EXAMPLE 21

As in Example 20 except the roller spacing was 80 micron. The O₂ and CO₂permeabilities prior to this treatment were 1.1×10⁻¹⁵ and 4.0×10⁻¹⁵mole.m⁻¹ s⁻¹ Pa⁻¹ and afterwards 0.9×10⁻¹⁵ and 3.4×10⁻¹⁵ mole.m⁻¹ s⁻¹Pa⁻¹.

EXAMPLE 22

A polyethylene film 15% low density and 85% linear low density wasfabricated according to PCT/AU91/00346 with 0.05% scoria. The intrinsicfilm thickness was 20 micron and the particle size was 50 to 75 micron.The film was processed with the rollers at ambient temperature and aroller spacing of 0 micron. The O₂ and CO₂ permeabilities prior to thistreatment were 2.5×10⁻¹⁵ and 6.7×10⁻¹⁵ mole.m⁻¹ s⁻¹ Pa⁻¹ and afterwards9.4×10⁻¹⁵ and 9.0×10⁻¹⁵ mole.m⁻¹ s⁻¹ Pa⁻¹.

EXAMPLE 23

As in Example 22 except the intrinsic film thickness was 30 micron. TheO₂ and CO₂ permeabilities prior to this treatment were 2.5×10⁻¹⁵ and6.7×10⁻¹⁵ mole.m⁻¹ s⁻¹ Pa⁻¹ and afterwards 3.3×10⁻¹⁵ and 7.2×10⁻¹⁵mole.m⁻¹ s⁻¹ Pa⁻¹.

EXAMPLE 24

As in Example 22 except the intrinsic film thickness was 50 micron. TheO₂ and CO₂ permeabilities prior to this treatment were 1.8×10⁻¹⁵ and5.6×10⁻¹⁵ mole.m⁻¹ s⁻¹ Pa⁻¹ and afterwards 2.3×10⁻¹⁵ and 6.0×10⁻¹⁵mole.m⁻¹ s⁻¹ Pa⁻¹.

EXAMPLE 25

As in Example 22 except the intrinsic film thickness was 80 micron. TheO₂ and CO₂ permeabilities prior to this treatment were 1.1×10⁻¹⁵ and4.0×10⁻¹⁵ mole.m⁻¹ s⁻¹ Pa⁻¹ and afterwards 0.96×10⁻¹⁵ and 4.2×10⁻¹⁵mole.m⁻¹ s⁻¹ Pa⁻¹.

EXAMPLE 26

As in Example 22 except the roller temperature was 80° C. The O₂ and CO₂permeabilities prior to this treatment were 2.5×10⁻¹⁵ and 6.7×10⁻¹⁵mole.m⁻¹ s⁻¹ Pa⁻¹ and afterwards 1.8×10⁻¹⁴ and 1.8×10⁻¹⁴ mole.m⁻¹ s⁻¹Pa⁻¹.

EXAMPLE 27

As in Example 26 except the intrinsic film thickness was 30 micron. TheO₂ and CO₂ permeabilities prior to this treatment were 2.5×10⁻¹⁵ and6.7×10⁻¹⁵ mole.m⁻¹ s⁻¹ Pa⁻¹ and afterwards 2.6×10⁻¹⁴ and 5.6×10⁻¹⁴mole.m⁻¹ s⁻¹ Pa⁻¹.

EXAMPLE 28

As in Example 26 except the intrinsic film thickness was 50 micron. TheO₂ and CO₂ permeabilities prior to this treatment were 1.8×10⁻¹⁵ and5.6×10⁻¹⁵ mole.m⁻¹ s⁻¹ Pa⁻¹ and afterwards 8.8×10⁻¹⁵ and 1.5×10⁻¹⁴mole.m⁻¹ s⁻¹ Pa⁻¹.

EXAMPLE 29

As in Example 26 except the intrinsic film thickness was 80 micron. TheO₂ and CO₂ permeabilities prior to this treatment were 1.1×10⁻¹⁵ and4.0×10⁻¹⁵ mole.m⁻¹ s⁻¹ Pa⁻¹ and afterwards 1.1×10⁻¹⁵ and 4.2×10⁻¹⁵mole.m⁻¹ s⁻¹ Pa⁻¹.

EXAMPLE 30

As in Example 29 except the roller spacing was 80 micron. The O₂ and CO₂permeabilities prior to this treatment were 1.1×10⁻¹⁵ and 4.0×10⁻¹⁵mole.m⁻¹ s⁻¹ Pa⁻¹ and afterwards 1.8×10⁻¹⁵ and 4.1×10⁻¹⁵ mole.m⁻¹ s⁻¹Pa⁻¹.

EXAMPLE 31

As in Example 22 except the roller temperature was 100° C. The O₂ andCO₂ permeabilities prior to this treatment were 2.5×10⁻¹⁵ and 6.7×10⁻¹⁵mole.m⁻¹ s⁻¹ Pa⁻¹ and afterwards 7.8×10⁻¹⁵ and 5.8×10⁻¹⁵ mole.m⁻¹ s⁻¹Pa⁻¹.

EXAMPLE 32

As in Example 31 except the intrinsic film thickness was 30 micron. TheO₂ and CO₂ permeabilities prior to this treatment were 2.5×10⁻¹⁵ and6.7×10⁻¹⁵ mole.m⁻¹ s⁻¹ Pa⁻¹ and afterwards 1.2×10⁻¹⁴ and 1.2×10⁻¹⁴mole.m⁻¹ s⁻¹ Pa⁻¹.

EXAMPLE 33

As in Example 31 except the intrinsic film thickness was 50 micron. TheO₂ and CO₂ permeabilities prior to this treatment were 1.8×10⁻¹⁵ and5.6×10¹⁵ mole.m⁻¹ s⁻¹ Pa⁻¹ and afterwards 2.1×10⁻¹⁵ and 4.9×10⁻¹⁵mole.m⁻¹ s⁻¹ Pa⁻¹.

EXAMPLE 34

As in Example 31 except the intrinsic film thickness was 80 micron. TheO₂ and CO₂ permeabilities prior to this treatment were 1.1×10⁻¹⁵ and4.0×10⁻¹⁵ mole.m⁻¹ s⁻¹ Pa⁻¹ and afterwards 1.1×10⁻¹⁵ and 4.2×10⁻¹⁵mole.m⁻¹ s⁻¹ Pa⁻¹.

EXAMPLE 35

38.7g(20 mL) of alumina, pore size 0.1μ, particle size 53-75μ, was mixedwith 260 g of low density polyethylene. 150 g of this master batch wasadded to 350 g of ultralow density polyethylene and film blown,thickness 27μ. The film was processed as described in example 1 at 90°C. with a roller spacing of 0μ. The permeability of the film to O₂ wasmeasured as 1.6×10⁻¹³ mole/m.s.Pa and to CO₂ was measured as 3.1×10⁻¹³mole/m.s.Pa.

EXAMPLE 36

The film as described in example 35 was processed at 105° C., with aroller spacing of 40μ, and the O₂ permeability found to be 1.9×10⁻¹³mole/m.s. Pa and the CO₂ permeability 1.8×10⁻¹³ mole/m.s.Pa.

EXAMPLE 37

22.6 g(20 mL) of alumina, pore size 0.01μ, particle size 53-75μ, wasmixed with 260 g of low density polyethylene. 150 g of this master batchwas added to 350 g of ultralow density polyethylene and film blown,thickness 21μ. The film was processed as described in example 1 at 90°C. with a roller spacing of 0μ. The permeability of the film to O₂ wasmeasured as 7.4×10⁻¹³ mole/m.s.Pa and to CO₂ was measured as 4.9×10⁻¹³mole/m.s.Pa.

EXAMPLE 38

The film as described in Example 37 was processed at 105° C., with aroller spacing of 40μ, and the O₂ permeability found to be 1.2×10-14mole/m.s.Pa and the CO₂ permeability 1.2×10⁻¹⁴ mole/m.s. Pa.

EXAMPLE 39

45.9 g(20 mL) of alumina, pore size 2μ, particle size 53-75μ, was mixedwith 360 g of low density polyethylene. 150 g of this master batch wasadded to 350 g of ultralow density polyethylene and film blown,thickness 35μ. The film was processed as described in example 1 at 90°C. with a roller spacing of 0μ. The permeability of the film to O₂ wasmeasured as 6.9×10⁻¹³ mole/m.s.Pa and to CO₂ was measured as 6.5×10⁻¹³mole/m.s.Pa mole/m.s.Pa.

EXAMPLE 40

The film as described in Example 39 was processed at 105° C., with aroller spacing of 40μ, and the O₂ permeability found to be 2.0×10⁻¹⁴mole/m.s.Pa and the CO₂ permeability 5.1×10⁻¹⁴ mole/m.s.Pa.

We claim:
 1. A process for preparing a controlled permeability filmwhich includes:providing a film forming polyolefin polymer; and an inertporous filler in an amount effect to reduce the ratio of CO₂permeability to the O₂ permeability of the film, and wherein the fillerhas a particle size greater than the intrinsic film thickness of thefilm forming polymer to be prepared: mixing the polyolefin polymer andinert porous filler at elevated temperature; forming the mixture into afilm of intrinsic thickness less than the particle size; and subjectingthe film to a permeability modifying step such that the CO₂ /O₂permeability ratio is reduced to approximately 0.5 to 2.0 wherein thepermeability modifying step includes a compression treatment comprisingapplying a compressive force to the film with a plate or roller, whereinthe compressive force is sufficient to thin or remove film formingmaterial between the filler particles and the atmosphere.
 2. A processaccording to claim 1 wherein the permeability modifying step is suchthat the CO₂ /O₂ permeability ratio is reduced to approximately 0.5 to1.5.
 3. A process according to claim 1 wherein the compressive force isin the range of approximately 2.5 kg to 100 kg.
 4. A process accordingto claim 1 wherein the compressive force is in the range ofapproximately 5 kg to 75 kg.
 5. A process according to claim 1 whereinthe permeability modifying step includes subjecting the film to auniaxial stretching, wherein the stretching force is approximately 2.5kg to 75 kg.
 6. A process according to claim 1 wherein the stretchingforce is approximately 5 kg to 50 kg.
 7. A process according to claim 1wherein the permeability modifying step is conducted at a temperature ofapproximately 10° C. to 200° C.
 8. A process according to claim 1wherein the permeability modifying step is conducted at a temperature ofapproximately 75° C. to 115° C.
 9. A controlled permeability filmproduced by a process according to claim 1, wherein the film includes:afilm forming polyolefin polymer; and an inert porous filler in an amounteffective to reduce the ratio of CO₂ permeability to O₂ permeability ofthe film; wherein the filler has a particle size greater than theintrinsic film thickness of the film forming polymer, the controlledpermeability film being further modified to reduce the CO₂ /O₂permeability ratio to approximately 0.5 to 2.0.
 10. A controlledpermeability film according to claim 9 wherein the CO₂ /O₂ permeabilityratio is further modified to approximately 0.5 to 1.5.
 11. A filmaccording to claim 9 wherein the polyolefin polymer is selected frompolyethylene and blends of polyethylene with polyesters, includingpolyethylene terephthalate and polybutylene terephthalate, vinylpolymers including polyvinyl chloride, polyvinyl acetate, ethylene-vinylacetate copolymers and ethylene-vinyl alcohol copolymers, polycarbonatesand polystyrenes and polyalkylene oxide polymers including polyethyleneoxide polymer.
 12. A film according to claim 9 wherein the film formingpolyolefin polymer is a low density polyethylene.
 13. A film accordingto claim 9 wherein the inert porous filler is selected form pumice,tuff, rhyolite, dacite, reticulite, scoria, lapilli, agglomerate,perlite, pumicite, volcanic rocks, natural zeolites or sandstones; coal,char, charcoal, starch, seaweed, polymeric carbohydrates; porousglasses, clays modified to produce porosity, cordierite, mullite;alumina, silica, zirconia, magnesia, cerium compounds; polyvinyl alcoholand polyacrylamide.
 14. A film according to claim 9 wherein the inertporous filler consists of pumice particles having a particle sizegreater than the intrinsic film thickness of film forming polymer.
 15. Afilm according to claim 9 wherein the inert porous filler consists ofalumina particles having a particle size greater than the intrinsic filmthickness of the film forming polymer.
 16. A film according to claim 9wherein the inert porous filler includes a surface modifying agentcoated thereon in an amount effective to modify the surface behaviour ofthe porous filler.
 17. A film according to claim 16 wherein the surfacemodifying agent renders the surface of the porous filler hydrophobic.18. A film according to claim 16 wherein the surface modifying agent isselected from polyethylene glycols, nonylaphenyl polyethylene oxide,polyvinyl alcohols, polyvinyl acetates, parafins, polysiloxanes andsilane coupling agents, metal alkoxides, alcohols and combinationsthereof.
 19. A controlled permeability film produced by the process ofclaim 1 wherein the film includes:a film forming polyolefin polymer; anda disbursing polymer and an inert porous filler in an amount effectiveto reduce the ratio of CO₂ permeability to the O₂ permeability of thefilm, and wherein the film has a particle size greater than theintrinsic film thickness of the composite film; the controlledpermeability film being further modified to reduce the CO₂ /O₂permeability ratio to approximately 0.5 to 2.0.
 20. A controlledpermeability film according to claim 19 wherein the inert porous filleris a modified porous filler including a surface modifying agent.
 21. Apackaged product including:a controlled permeability film as defined inclaim 9, and a product packaged therein.
 22. A packaged productaccording to claim 21 wherein the product is selected from broccoli,brussel sprouts, beans, cabbage, chicory, celery, cauliflower, radish,artichoke, lettuce, tomatoe, pepper, leeks, parsley, spinach, asparagus,mushroom, okra, flowers, berries, cherries, melons, mango, papaya,pineapple, avocado, persimmon, grapefruit, kiwi fruit, nectarine, peach,apple, banana, orange, apricot, grape, cranberry, plum, pear and nashi.23. A packaged product according to claim 21 wherein the product isselected from nematodes, live aquatic animals, live aquatic plants andaerobic microorganisms.
 24. A composite packaging article including acontrolled permeability film as defined in claim 9; anda packaging filmadhered along at least one edge thereof to the controlled permeabilityfilm.
 25. A composite packaging article according to claim 24 wherein asachet including a gas sorbing or generating material is attached to asurface of the controlled permeability film.